Microwave switching device



June 5, 1962 G. s. UEBELE ETAL 3,038,131

MICROWAVE SWITCHING DEVICE 4 Sheets-Sheet 1 Filed Nov. 25, 1958 GeorgeS. Uebele,

Neal C. Silence,

INVENTORS June 5, 1962 e. S.IUEBELE ETAL 3,038,131

MICROWAVE SWITCHING DEVICE 4 Sheets-Sheet 2 Filed Nov. 25, 1958 GeorgeS. Uebele, Neal C SIIGI'ICG,

INVENTORS.

A T TOR/V5 Y.

June 5, 1962 G. s. UEBELE ETAL 3,038,131

MICROWAVE SWITCHING DEVICE 4 Sheets-Sheet 3 F lg. 8.

Filed Nov. 25, 1958 'l v Field intensities needed for suturo'flon.

Flux density needed for -45 romilon.

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78 Ferrite Fig 10.

Ferrite PULSE CIRC'UIT\42 m e b m en m a 0 6C 9 N mmw eN GN ATTORNEY.

June 5, 1962 G. s. UEBELE ETAL 3,038,131

MICROWAVE SWITCHING DEVICE 4 Sheets-Sheet 4 Filed Nov. 25, 1958 GeorgeS. Uebele, Neal C. Silence INVENTORS.

ATTORNEY.

United States Patent Ofi ice 3,fi38,l3i Patented June 5, 1962 3,038,131MICROWAVE SWITCHING DEVICE George S. Uebele, Long Beach, and Neal C.Silence, Torrance, Calif., assignors to Hughes Aircraft Company, CulverCity, Calif., a corporation of Delaware Filed Nov. 25, 1958, Ser. No.776,386 4- Claims. (Cl. 333-7) This invention relates to microwavetransmission and control devices, and particularly to switching deviceswhich utilize magnetized ferromagnetic elements.

Electronic devices which operate in the microwave region of thefrequency spectrum and which utilize the gyromagnetic properties ofcertain ferromagnetic elements are being increasingly employed. As isnow well known, magnetized ferromagnetic elements within a microwavetransmission or propagation device can be employed to provide a numberof effects which have wide utility in microwave systems. Thus, when aferroma netic element is positioned along the central axis of the hollowwaveguide and subjected to an axial magnetic field, there may beprovided a rotation of plane polarized energy within the waveguide whichcan be compared to the Faraday rotation earlier observed in the opticalregion of the spectrum. This class of devices is in fact usuallyreferred to as employing Faraday rotation. When polarization sensitiveelements are used with these Faraday rotators, the result may be aswitching arrangement or an energy circulating arrangement or one of thevarious other forms of energy controlling devices utilized in microwavesystems.

The arrangements heretofore provided for the establishment of thedesired magnetic field within an active ferromagnetic element havesuffered from certain disadvantages which have usually imposed operatingor economic limitations on the systems in which the devices are used.With the Faraday rotation type devices, for example, it may be desiredto switch energy at extremely high rates of speed but with closelycontrolled accuracy. When the magnetic field applied to theferromagnetic element varies, however, there is subsequent variation inthe angular rotation within the waveguide, so that the polarizationsensitive outputs derive varying amounts of energy. In many instanceseven a slight deviation in the amount of energy derived will have anappreciable effect upon the reliability of the information which thesystem is processing. In many instances extreme measures have had to betaken to overcome these inaccuracies. complicated circuits have beenevolved to hold the magnetizing currents constant. The use of thesecontrol arrangements does not always insure sufiicient accuracy, andeven when it does may be objectionable from the standpoints of size andeconomy.

An object of this invention is to provide a switching arrangement formicrowave systems which operates with a minimum of current and whichavoids the need for regulating circuits.

An arrangement constructed in accordance with this invention mayutilize, as a principal feature, a ferromagnetic element disposed in ahollow waveguide. If centrally disposed, the ferromagnetic element maybe arranged to provide Faraday rotation of energy transmitted along thewaveguide. A magnetic return path structure may be disposed within thewaveguide, at least partially encompassing the ferromagnetic element andproviding a low reluctance medium for a substantial part of the axialmagnetic field through the ferromagnetic element. At least one of thetwo magnetizable elements, the ferromagnetic element and the return pathstructure, may be constructed of a material having substantial magneticretentivity. Specifically, the selected member may have a residualmagnetic field, after being driven to saturation,

Thus,

which is sufiicient to provide a static magnetic field through theferromagnetic element of enough magnitude to provide a desired degree ofFaraday rotation of energy transmitted along the waveguide. Inconjunction with this arrangement may be employed a driving coil affixedto the return path structure. The application of a driving pulse ofselected magnitude and direction through the driving coil thus providesa sufficient magnetic field of proper direction through the activeferromagnetic element to provide a desired Faraday rotation withoutfurther circuitry being needed. A further feature resides in the use ofa static magnetic bias to establish zero net magnetization of the activeelement when no Faraday rotation is to be used. The static bias permitsthe use of driving currents which establish saturation, rather than moreprecisely controlled currents to establish demagnetization.

In accordance with other features of this invention, the arrangementabove described may be utilized to provide various forms of switchingand circulating arrangements having particular advantages. The energymay be rotated from a given direction 45 degrees in either direction tobe provided as output to either one of two polarization sensitiveterminals. A fixed biasing field, equivalent to 45 degrees of rotation,may be superimposed on a ferromagnetic element and the residual magneticfield used to augment or cancel this rotation, so that rotation of fromzero to degrees is provided. In another arrangement, the retained fieldmay be utilized together with a ferromagnetic element positioned withina short circuited, reflecting waveguide section, and the magnetic fieldestablished may be substantially completely defined by the activeferromagnetic element and the enclosing return path structure. Inaccordance with other features of this invention, the ferromagneticelement itself may be a composite structure consisting both of activeferromagnetic materials and other materials which may have appreciablemagnetic retentivity and be arranged in a combination to providesufficient rotation through the use of pulsing currents and residualmagnetism. Various forms of transverse field devices for rectangularwaveguide may be provided. Arrangements thus constructed in accordancewith this invention may be utilized as switches and energy transferdevices including duplexing and circulating arrangements.

The novel features of this invention, as well as the invention itself,may be better understood from the following description, taken inconjunction with the accompanying drawings, in which like referencenumerals refer to like parts, and in which:

FIG. 1 is a perspective view, partially broken away, of a microwaveenergy switch in accordance with the invention;

FIG. 2 is a side sectional view of the arrangement of FIG. 1;

FIG. 3 is an end sectional view of the arrangement of FIG. 1, takenalong the lines 33 in FIG. 2 looking in the direction of the arrowstherein;

FIG. 4 is a side elevation view of a second arrangement in accordancewith the invention utilizing an internal coil and a ferromagneticcylinder within a Waveguide and encompassing a central ferrite member;

FIG. 5 is a side sectional view of the arrangement of FIG. 4, showinginternal details of the arrangement;

FIG. 6 is a fragmentary view of the central portion of the arrangementof FIG. 5, showing the ferromagnetic cylinder and the central ferritepencil;

FIG. 7 is an end view of the arrangement of FIGS. 4-6, taken along theline 7-7 in FIG. 5, and looking in the direction of the arrows;

FIG. 8 is a graph of the magnetization characteristics a of ferritematerials which may be employed in accordance with the invention;

FIG. 9 is a simplified perspective view, partially broken away, ofanother arrangement in accordance with the invention, utilizing theretentive properties of a return path element for magnetizing an activeferromagnetic element;

FIG. 10 is a simplified elevation view of another arrangement inaccordance with the invention utilizing the retentive proper-ties of amagnetic material to achieve Faraday rotation;

FIG. 11 is a side sectional simplified view of another arrangement forachieving Faraday rotation in accordance with the invention, and

FIG. 12 is a perspective view, simplified and partially broken away forpurposes of illustration, exemplifying an arrangement in accordance withthe invention for providing transverse field operation with aferromagnetic element in a microwave waveguide.

An arrangement in accordance with the invention, referring now to FIGS.1, 2 and 3, may utilize a ferrite element within a microwave waveguide,in conjunction with magnetic field elements within the waveguide, toestablish a desired energy rotation of microwave energy upon theapplication of a pulsing current. The arrangement may include anorthogonal mode transducer 10 using a square waveguide body 11 having acentral longitudinal axis. To the square waveguide body 11 may becoupled a first rectangular input waveguide 12 which is colinear withthe square waveguide body 11 and which has its broad walls parallel to aselected pair of the Walls of the square waveguide body 11 and the firstrectangular waveguide 12 to provide, for energy supported in thedominant mode of the first rectangular waveguide 12, a smooth transitionto the equivalent mode in the square waveguide body 11. A secondrectangular waveguide may be coupled to one of the walls of the squarewaveguide section 11 which is coplanar with the broad walls of the firstrectangular waveguide 12. The central aXis of the second rectangularwaveguide 15 is normal to the axis of the square waveguide body 11, andthe broad walls of the second rectangular waveguide 15 lie in planesparallel to the narrow walls of the first rectangular waveguide 12.

The square waveguide body 11 supports orthogonally disposed energy modes(modes which are normal and independent with respect to each other). Theorthogonal mode transducer 10 operates to divert each of theseindividual modes to a selected one of the first and second rectangularwaveguides 12 and 15 respectively. To this end, the broad wall of thetransducer 10 to which the second rectangular waveguide 15 is coupledincludes a coupling slot 16, and the transition section defined by thestep sections 13 includes a centrally disposed conductive septum 18. Theseptum 18 lies in a plane which is substantially normal to the vectorialcomponents of the dominant mode supported within the first rectangularwaveguide 12. Energy in a first direction of linear polarization, normalto the broad walls of the first rectangular waveguide 12, is transferredthrough the square Waveguide body 11 without passing out the couplingslot 16 to the second rectangular waveguide 15. Energy transmitted inthe opposite direction, and with a like polarization, similarly does notexcite the coupling slot 16 and is not affected by the conductive septum18, so that it is returned out the first rectangular waveguide 12.Energy supported in the second rectangular waveguide 15 excites thecoupling slot 16 but sees an effective short circuit at the conductiveseptum 18 and is accordingly transferred through the square waveguidebody 11. This energy is, however, orthogonal with respect to thatpreviously discussed. Energy having the second direction of polarizationtransferred into the square waveguide body 11 is directed out the secondrectangular waveguide 15 alone.

Consequently, the operation of the orthogonal mode transducer 10 is tocouple energy of different polarizations from the separate waveguidearms 12 and 15 to the common body 11. Energy provided to the squarewaveguide body 11 is effectively switched either to the firstrectangular waveguide 12 or to the second rectangular waveguide 15,dependent upon the direction of polarization of the energy. In thepresent example, it is assumed that energy provided to the firstrectangular waveguide 12 is to be the input to the associated microwavedevice. Outputs may be taken either from the first rectangular Waveguide12 or the second rectangular waveguide 15, depending upon whichassociated microwave device (not shown) of the related microwave systemis to be employed. Conventional flanges may be employed at the variousextremities of the orthogonal mode transducer 10 for coupling to theassociated waveguide or other microwave elements.

With the orthogonal mode transducer 10 may also be employed a reflectivemicrowave device which includes means for selectively rotating thedirection of polarization of the microwave energy. This arrangement mayinclude a square waveguide section 20 which terminates at its endopposite to the orthogonal mode transducer 10 in a conductive reflectingplate 21. The square waveguide 20 is capable of supporting microwaveenergy in various positions of rotation and is colinear with and hasinternal dimensions like the square waveguide body 11 of the orthogonalmode transducer 10. Additionally, this square waveguide 20 may be arigid waveguide, having four ridges 22 (best seen in FIGS. 2 and 3)extending from the walls of the waveguide 20 toward the central axis ofthe waveguide. The square waveguide section 20 may be coupled to thebody portion 11 of the orthogonal mode transducer 10 by a squarewaveguide coupling section 24 having matching internal dimensions andimpedance matching transition ridges 25 (best seen in FIG. 2). Theimpedance matching transition ridges 25 consist of successive steps 26and 27 between the full ridges 22 in the square waveguide 20 and theunridged body 11 of the orthogonal mode transducer 10. Each of thetransition ridges 25 registers with a different one of the ridges 22 ofthe square waveguide 20 and lies in the same plane as the associatedridge 22. The transition section 24 may be coupled by flanges to boththe orthogonal mode transducer 10 and the square waveguide section 20.It will be understood, however, that this arrangement is provided forsimplicity and ease of manufacture, and that if desired the squarewaveguide section 20 may be coupled directly to the orthogonal modetransducer 10 or that other forms of transition sections might beutilized. The sections shown, however, may be readily assembled and whenconstructed in the manner indicated consist of separate parts which maybe individually fabricated quite simply.

With the square waveguide 20 thus constructed, there is a centralaperture defined by the innermost surfaces of the ridges 22. Within thisaperture, and along the central axis of the square waveguide 20 may beplaced an elongated rod or pencil of ferromagnetic material 30. Theferromagnetic pencil may have an impedance matching taper 31 at its endclosest to the orthogonal mode transducer 10 and may abut the conductivereflecting plate 21 at the other end. The term ferromagnetic is hereemployed to designate the class of materials, including ferrite andgarnet type materials, which have the effects on microwave energypreviously mentioned, when combined with appropriate magnetic fields.The arrangement of the ferromagnetic pencil 30, which is in thisinstance assumed to be ferrite, is here intended to provide Faradayrotation of energy within the square waveguide 20.

The varying magnetic field to be applied through the ferrite pencil 30to achieve Faraday rotation is, as indicated above, an axial magneticfield, and one which extends in this instance along the central axis ofthe square waveguide 20. The means for establishing this magnetic fieldis one of the important features of the present exemplification of theinvention. The internal ridges 22 of the square waveguide 20 have cutoutportions 33 adjacent the walls of the waveguide 20. These cutoutportions 33 are defined by a reduction in the outer dimension of theridges 22, the cutouts extending from the reflecting plate 21 for adistance along the length of the ferrite pencil 30. The walls of thesquare rwaveguide 20 may at this point be comprised of relatively thinwall sections 34 coextensive with the cutout portions 33. Thus betweenthe thin wall sections 3 3 and the cutout portion 33 of the ridges 22there may be considered to be a volume conforming to the walls of thewaveguide 20 and extending therearound.

Within this volume defined by the cutout portions 33 and the thin wallsections 34 may be positioned an arrangement for providing both theestablishment and maintenance of the desired magnetic field. A number ofstrips 36 of material having selected magnetic properties may extendparallel to the waveguide 26 axis and adjacent to the thin wall sections.34. The strips as may abut the reflecting plate 21 and be coextensivewith a principal portion of the length of the ferrite cylinder 3%. Asbest seen in FIGS. 1 and 3, these strips 36 may be grouped adjacent thecorners of the waveguide 20. Within the structure thus formed and havinga like square section, when viewed along the axis of the waveguide 20,may be a conductive coil 38 wound to define a helix having its axiscoextensive with the axis of the waveguide 20. The helical coil 38 mayin turn be wound upon and supported by a rectangular form 39 concentricwith the waveguide 20 and contacting the cutout portions 33 in theridges 22. The support form 39 thus sup ports the helical coil 38 whichin turn supports the magnetizable strips 36. This arrangement may bereferred to as a return path structure for the magnetic field throughthe ferrite pencil 30. The support form 39 is preferably of a materialwhich is substantially transparent to microwave energy. Leads 4t? fromthe helical coil may be coupled to an external source of a drivingcurrent, which in this instance is given the general designation of apulse circuit '42. The pulse circuit 42 may be any conventional drivingcircuit for applying a momentary current of desired magnitude to thehelical coil 38.

Positioned adjacent the reflecting plate 21 and extending diagonallyfrom the ferrite pencil 30 to each corner of the return path structuremay be a different magnetizable cross piece 44. The magnetizable crosspieces 44- may have one end registering with the ferrite pencil 30 andthe other end shaped to register with the associated magnetizable stripsas, and may be fixed, as by an adhesive, to the reflecting plate 21.

The magnetizable structure thus formed defines a substantial portion of-a magnetic flux path. The magnetic flux extends axially and centrallyalong the waveguide 20 within the ferrite pencil 30, and may bevisualized as extending out through the cross pieces 44 and extendingthrough the strips 36. The direction of the flux is of course dependentupon the direction of magnetization. Between the ends of strips 36 andthe tapered end 31 of the ferrite pencil 30 there may be seen to be amagnetic gap which will be discussed later. A static biasing fieldextending longitudinally through the ferrite pencil may be establishedby a permanent or electromagnet. Here a permanent magnet 46 is providedfor purposes of illustration, the permanent magnet as being a bar magnetaffixed to a wall 34 of the waveguide 20. The strength and direction ofthe magnetic field created by the permanent magnet 46 is determined inaccordance with considerations given below. This static biasing field iscompleted axially through the ferrite pencil 30 in part through thepresence of the magnetic gap. Thus shunt felds can be minimized oravoided.

The magnetic retentivity of the material in the ferrite strips 36 and inthe cross pieces 44 is here arranged to have important operatingsignificance. Specifically, the residual magnetism of the ferrite strips36 is such that in the arrangement with the ferrite pencil 30 and withthe biasing field a suflicient static magnetic field can be provided toachieve desired amounts of rotation of microwave energy. In this sense,the ferrite pencil 30 may be considered to be the active element, andthe return path cylinder a static element which makes possible theFaraday rotation achieved by the active element. It is clear that theintensity of the magnetic field provided by the return path cylinder isdependent both upon the retentivity of the magnetizable strips 36 andthe cross pieces 44 and upon the volume and configuration of thematerial contained in the return path cylinder, as well as the magneticgap. While FIGS. 1, 2 and 3 are not drawn to scale, the approximaterepresentations shown have been found to provide proper flux paths forthe operation described below.

The material which may be employed for the ferrite strips 36, or forboth the ferrite strips 36 and the cross pieces 44, may be one of anumber of difierent types of material which are relatively hardmagnetically and which can retain an appreciable portion of theirmagnetism when the magnetic applied field is removed. These materialsare not so magnetically hard, however, as to require significantlyhigher magnetic fields in order to have a change in their condition ofmagnetization. A number of different ferromagnetic compositions. isavailable for this purpose, including a number of the ferrite materialsand a number of ferrous materials. In the present example it is assumedthat the magnetizable elements 36 and aid will be driven to saturationin one direction. The amount of magnetization retained after saturationand in the absence of an applied external field, except for the staticfield, is therefore determinative of the strength of field applied tothe active element. This is pointed out in order to further recognizethe fact that the volume and configuration of the magnetizable elementsmay have to be altered if a different material, having differentretentivity, is employed.

In the operation of the arrangement of FIGS. 1, 2 and 3, it is desiredto switch input energy provided from the first rectangular waveguide 12back to the first rectangular waveguide 12, or selectively, to providesuch energy to the second rectangular waveguide 15. Thus the firstrectangular waveguide 12 serves both as an input and one output formicrowave energy, and the second rectangular waveguide 15 serves as theother output. Such arrangements have wide utility in microwave systemsin switching different signals to different elements or in divertinghigh power signals to a different channel than low power signals. Theswitching action in the present instance is to be accomplished undercontrol of the pulse circuit 42. and the biasing magnet 46. When energyis to be re turned back to the first rectangular waveguide 12 output,the ferrite pencil 30 is to have zero net magnetization. For thiscondition of operation it is assumed that a reset condition haspreviously been established. When the energy is to be switched to thesecond rectangular waveguide 15 as output, therefore, a pulse isprovided to effect the switching action. Output thereafter is providedfrom the second rectangular waveguide 15, until a reset signal isprovided from the pulse circuit 42 to return the active ferrite elementto zero net magnetization.

In operation, linearly polarized input energy having a direction ofpolarization supported by the dominant mode Within the first rectangularwaveguide 12 is provided through that waveguide through the orthogonalmode transducer 10. Such energy does not, as described above, coupleinto the second rectangular waveguide 15 but passes into the transitionsection '24 and then into the square waveguide section 20. In theabsence of a magnetic field in the return path cylinder and the ferritepencil 30, such energy is simply reflected from the reflecting plate 21back through the square waveguide section 20, the transition section 24and the orthogonal mode transducer 10* to the first rectangularwaveguide 12.

When a magnetizing pulse of sufficient amplitude is pro vided from thepulse circuit 42, however, the ferrite strips 36 and the cross pieces 44are momentarily driven to saturation in the selected direction.Thereafter the pulse is terminated and the residual magnetic fieldretained. The net magnetic field consists both of the residual magneticfield within the strips 36 and cross pieces 44 and the static biasingfield created by the permanent magnet 46 and extending through themagnetic gap and the ferrite pencil 30.

The driving pulse need only be a fraction of a microsecond to establishthe saturation magnetization and the desired retained magnetic field.This magnetic field is substantially completely within the squarewaveguide 20 and extends through the ferrite strips 36, the cross pieces44, the ferrite pencil 30 and between the tapered end 31 of the ferritepencil 30 and to the adjacent ends of the ferrite strips 36. Because theferrite strips 36 are grouped at the separate corners of the squarewaveguide 20, the flux path for the retained field is similarlyconcentrated. The presence of the cross pieces 44 further contributes tothe low reluctance path for the retained magnetic field, and it is foundthat the magnetic circuit thus provided is extremely efficient. Thedirection of the magnetic field existing within the active element, theferrite pencil 30, is selected in the direction which is desired. I11the present instance, either one of the directions of rotation may beutilized. The intensity of the net magnetic field established in thestatic condition is selected to be such that a 45 degree rotation ofmicrowave energy is provided by the ferrite pencil 30. The net magneticfield is determined by the static field established as a result of theoperation of the pulse circuit 42 and the static biasing field generatedby the permanent magnet 46. In the selected direction of magnetizationfor energy rotation, the biasing field tends to increase the netmagnetic field, because the biasing field is utilized to cancel theretained field in the opposite direction of magnetization. A furtherdescription of this relationship is given below. The net field, however,can be established at a desired level and adjustments can be made byvariation of the length of the ferrite pencil 30 or other means.

Upon establishment of the desired magnetic field in the return pathcylinder by passage of the driving pulse through the coil 38, therefore,microwave energy from the input is rotated Within the square waveguidesection 20. This rotation is 45 degrees and may in the present instancebe assumed to be clockwise, as viewed from the input end of the device.This 45 degree rotation is only that provided by transmission past theferrite pencil 30 in one direction, however. In effect, the energyreflected from the reflecting plate 2.1 has been rotated 45 degrees.Because of the nonreciprocal nature of ferromagnetic materials, however,the microwave energy is rotated a further 45 degrees as it istransmitted along the waveguide back toward the input end. This featureenables the utilization of a lesser magnetic field when rotation is tobe provided.

The energy provided back from the square waveguide 20 and the transitionsection 24, therefore, is orthogonal with respect to the input energy.Such energy sees an effective short circuit at the conductive septum 18within the orthogonal mode transducer and furthermore excites theradiation aperture 16 coupled to the second waveguide arm 15.Accordingly, such energy is switched out the second waveguide arm 15. Ifthereafter it is desired to switch back to the first condition ofoperation, in which inputs are reflected back, the pulse circuit 42 needonly establish saturation of the retentive element in the oppositedirection. A momentary pulse of sufficient amplitude through the coil'38 to drive the ferrite strips 36 and cross pieces 44 to saturationwill thereafter provide a retained static magnetic field of oppositepolarity. The net magnetic field, however, which is the sum at theferrite pencil 30 of the retained field and the static biasing 8 field,is arranged to be zero, so that no rotation is provided and signals arereturned to the input 12.

The advantages of this arrangement will now be apparent. In thisconnection, it should be noted that the use of the ridges 22 within thesquare waveguide 20 appreciably decrease the frequency sensitivity ofthe arrangement. Further, the use of the steps 26 and 27 in thetransition ridges 25 appreciably decrease insertion losses andreflective effects which might otherwise be present. It is of particularsignificance, moreover, that the switching can be accomplished with verybrief switching pulses in the manner indicated. With this arrangement,there is no need for a regulated current supply, as is required by thedevices heretofore available. As a consequence the complexity of theassociated equipment may be markedly decreased.

The regulating problems associated with providing a precise drivingcurrent for a period of time and under widely varying environmentalconditions are substantially completely obviated. The driving pulsesutilized'need not be closely controlled and can be provided very simplyby the discharge of signal storage devices. All that is required is avery brief driving pulse, which can be of the order of a microsecond orless, and which is of magnitude sufficient to establish saturation. Thepulse can also be greater than the magnitude needed for saturation, andthus need not be precisely controlled. The use of the static biasingfield is in this respect significant. The static biasing field can begenerated very simply, as with the permanent magnet shown, butnevertheless can be very accurate. In this respect, the magentic gapwhich is utilized provides an important feature. With a closed magneticpath it might be difiicult to establish the desired static biasingfield, and to have the proper operative relationships when the field isshifted from one state to another. It will be recognized that this samearrangement could be used with different angles of rotation, and that ifa reflective short circuit element is not to be utilized there can stillbe controlled switching of energy between different terminals. Incombination with these features, use of an internal return path cylinderand a configuration which is very easily fabricated permits theprovision of an extremely fast acting microwave switch of generalapplication.

Another arrangement in accordance with this invention may achieveeffective use of the retentivity of magnetizable material in combinationwith a pulsing source in a microwave device in a different manner. Thearrangement illustrated in FIGS. 4-7, to which reference is now made,may be arranged as a circulator. It employs a first orthogonal modetransducer 50, a second orthogonal mode transducer 54, and anintermediate waveguide body 58. The first orthogonal mode transducer 50may consist of a square to rectangular transition, as described ingreater detail in the arrangement of FIG. 1, and may include a firstrectangular terminal 51 and a second rectangular terminal 52 which isorthogonal with respect to the first. The second orthogonal modetransducer 54 may also be a transducer between a square waveguide andindividual rectangular waveguides. In this instance, however, therectangular waveguides may be disposed diagonally with respect to thesquare waveguide. Thus the second orthogonal mode transducer may includea third rectangular terminal 55 which is rotated 45 degrees clockwise(as viewed from thefirst rectangular terminal 51) and a fourthrectangular terminal 56 which is also rotated 45 degrees clockwise (asviewed from the second rectangular terminal 52). This arrangement isoften employed in circulator devices when coupled, as is shown here, byan intermediate waveguide body 58 which includes means by whichnonreciprocal rotation of energy may be achieved.

The waveguide body 58 is essentially a ridged square waveguide section.The square waveguide may consist of a pair of square waveguide bodies 59and 60, each of the walls of which has a longitudinal slot and each ofwhich is coupled to a different one of the orthogonal mode transducers50 or respectively. The square waveguide structure may be completed by acentral coupling structure consisting of a hollow square box member 62.The elements of the orthogonal mode transducers 5t) and 54, thewaveguide bodies 59 and 6t) and the box member 62 are thus colinear. Theridges 66 provided within this square waveguide may be formed byT-shaped segments (best seen in FIG. 6) with the top of the Ts restingon the outer surfaces of the waveguide portions 59 and 6d and the legsof the Ts being the ridge segments 66. As shown, each of the ridgesegments 66 may be coextensive with the waveguide body 58 and each maytaper to the associated inner surface of the walls of the waveguide body58 in each longitudinal direction. Transition sections 67 at each end ofthe ridges 66 provide a smooth transition for the passage of microwaveenergy within the waveguide body 58. The ridge sections 66 also includecutout portions 69 in their surfaces which are adjacent the walls of thewaveguide body 58. These cutout portions 69 are centrally disposed withrespect to the ridge sections 66 and to the waveguide body 58. Thus thecutout portions 69 define a central aperture concentric with the axis ofthe waveguide body 58 and extending around the waveguide body adjacentthe box member 62.

Within this inner surface aperture is positioned a magnetizing andreturn path structure comprising a support form 70 which is preferablyof a material substantially transparent to microwave energy and which isin contact with the cutout portions 69 in the ridges 66. A magnetizingcoil 72 consisting of a conductive wire may be wound upon the supportform 70, to have, like the support form 7d, a hollow square crosssection when viewed along the axis of the wavegniide body 53. Thewinding of the magnetizing coil 72 is however helical with respect tothe waveguide axis. Of like cross section, but encompassing themagnetizing coil 72 within the cutout portions 69 may be a return pathstructure 73 comprised of magnetizable material. Leads 74 may extendfrom the magnetizing coil 72 to a pulse circuit 76 which can providemomentary pulses of substantially selected amplitude and polarity, as isdescribed in greater detail below.

A ferrite pencil 78 having tapered ends 79 may be positioned within thecentral aperture defined by the innermost portions of the ridgedsect-ions 66. The ferrite pencil is, as described in the arrangementfirst discussed, active in the Faraday rotation sense. Additionally,however, it is desired to use a ferrite material which provides magneticretentivity as well as active microwave properties. This arrangement ismade useful through its employment with a magnetizing structure and thereturn path internal to the waveguide.

The operation of the device which is illustrated in FIGS. 4-7 may beviewed as a Faraday rotation action, or in conjunction with theassociated orthogonal mode transducers 56, 54, as a circulator action.Assuming that a 45 degree rotation is provided Within the waveguide body58, in a clockwise direction as viewed from the first rectangularterminal 51, the circulator action is as follows. Energy from the firstterminal 51 is transferred out the third terminal 55. Energy from thethird terminal 55 is, however, returned to the second rectangularterminal 52. Conversely, energy from the second terminal 52 is coupledout the fourth terminal 56, while energy from the fourth terminal $6 isreturned to the first terminal 51. If the direction of magnetization ofthe ferromagnetic element is reversed and the Faraday rotation is givenan opposite sense energy from the first terminal 51 is applied to thefourth terminal 56, and so on. This action remains the same and theFaraday rotation operation may be considered independently.

In the present arrangement the volume and disposition of the ferritepencil 78 with respect to the return path structure 73 is again such asto establish and maintain an accurate static magnetic fieldindefinitely, once a driving pulse has been applied. The pulse circuit76 provides a driving pulse of sufficient polarity and amplitude todrive the ferrite pencil 78 to saturation magnetization in a desireddirection. The retentivity of the ferrite pencil maintains a given fieldstrength following the termination of the magnetizing pulse. Thiseffective field is kept at sufficient flux density to maintain theFaraday rotation action through the employment of the return pathstructure 73. A number of ferromagnetic materials are available whichhave suificient retentivity as well as active properties. Therelationship which should be established is determined by the length ofthe ferrite pencil 78, its volume, the extent of its magneticretentivity, and the proximity and volume of the associated return pathstructure 73. Clearly, the return path structure 73 may itself haveappreciable magnetic retentivity. In the present example, however, whilethe drawings are not to scale it has been found that the approximateconfiguration shown provides sufficient effective magnetization tomaintain the desired 45 degree Faraday rotation of microwave energy.

In a practical embodiment of this invention, an active ferrite pencil 78of .250 inch diameter and 3 inches length Was employed in a 0.8 inch by0.8 inch waveguide having ridges .270 inch high. Fifty-eight turns ofNo. 27 wire were employed in the magnetizing coil 72. A ferrite materialwas used for the return path structure 73.

A number of other considerations also contribute to the advantageousoperation of this arrangement. The tapered ferrite pencil and theassociated return path structure 73 and the magnetizing coil 72 are sodisposed as to introduce little insertion loss and reflective effectswithin the waveguide body 58. The use of the ridges 66 not only providesa broader band operation, where a frequency range is to be utilized, butalso provides a ready means for positioning the ferrite pencil 78 andfor holding the magnetizing coil 72 and the return path structure 73.

Again, however, an important feature of this arrangement resides in thefact that while the associated circuitry is greatly simplified thedevice can provide substantially constant operation. The pulses appliedneed not be precisely controlled, because they need only exceed thesaturation magnetization level. Further, they can be of extremely shortduration, and thus very precisely mark the initiation of the time atwhich switching is to take place. Furthermore, the switching actionprovided is positive in both directions, being dependent only upon theselection of the direction of rotation which is desired. It has beenfound that the degree of rotation which results is extremely accurateand maintained substantially indefinitely Without change. Thus, asabove, the need for a current control is eliminated.

The operation of these devices in response to-a pulse source of currentmay be better understood with reference to FIG. 8. The graph of fluxdensity vs. field intensity there shown is the hysteresis loop for aferromagnetic material having the desired retentive properties. The loopis of the general form encountered with ferromagnetic materials, andprovides the desirable properties for an arrangement of this nature.FIGURE 8 is the curve which exists for a closed magnetic loop. With anair gap in the device the hysteresis loop would be of a slightlydifferent form, and would usually be less upright. The crossing lines ofthe hysteresis loop relative to the flux density, for the ferromagneticdevice containing an air gap, would be at a lower density. With the useof a static biasing magnet, however, the net flux density in thepolarity which is used for rotation will add the biasing flux to theretained flux to achieve the amount of flux needed for a selected degreeof rotation. With the retained field being of opposite polarity, thisstatic biasing fiux could effectively cancel the retained flux. Thevariable introduced by the length of the ferrite can be adjusted toinsure the proper amount of rotation. The field intensity required toestablish saturation magnetization is not excessive as would be the casein an extremely hard magnetic material. Nevertheless, an appreciableflux density exists when the magnetic field is removed, so that theretentivity can be used to provide active Faraday rotation properties ina ferrite itself or in some other member of a flux path structure.

A different arrangement having desirable properties for otherapplications is illustrated in simplified form in FIG. 9. Thisarrangement utilizes a constant biasing field through the activeferromagnetic element, together with a controllable field establishedthrough the retentive material which either augments or cancels thebiasing field. In this arrangement, energy from a source of planepolarized energy 80 may be provided through a switch section 81 to arotation section waveguide 82 which is here shown as circular. Outputsfrom the circular waveguide 82 are provided to either one of twopolarization direction sensitive microwave circuits. A first of theseoutput circuits 83 is coupled through a circular to rectangulartransition 84 in such fashion as to pass microwave energy having thesame direction of polarization as the input energy. A second outputcircuit 86 is coupled through a rectangular Waveguide 87 so as toextract from the circular waveguide 82 energy which has been rotated 90degrees from the original input direction of polarization.

Within the circular waveguide 82 is employed a Fara day rotation devicein accordance with the features of the present invention. An elongatedferrite pencil 90 supported by disks 91 which are substantiallytransparent to microwave energy, is positioned axially along thecircular waveguide 82. A magnetic return path cylinder 92 is positionedbetween the disks 91 and concentric with the ferromagnetic pencil 90.The return path cylinder 92 is of magnetizable material and completesthe flux path with the ferromagnetic pencil 90 within the waveguide 82.In the present example, the ferromagnetic pencil 90 has the desiredmagnetic retentivity, although either or both members of the flux pathstructure could have such properties. On the inner surface of the returnpath cylinder 92 may be a magnetizing coil 93 dis posed on a supportform 94 in a fashion similar to the arrangement described in conjunctionwith FIGS. 4-7. The arrangement of the return path cylinder 92, the coil93 and the inner support 94 will accordingly not be described in greaterdetail. Leads from the coil 93 extend to an external pulse source 95. Anexternal bias coil 96 may also be wound about the waveguide 82, todefine a helical coil structure with respect to the axis Waveguide 82.The terminals of the external bias coil 96 may be coupled to a fixedcurrent source 97. The external bias coil 96 is comparable to thepermanent bias magnet of the arrangement of FIG. 1. It will beunderstood that different magnetic field generating devices could beemployed to provide the desired static biasing field, as long as thefield is of sufiicient density and in a proper direction through theferrite element.

In the present example, it is desired either to pass nonrotated energythrough the circular waveguide 82 to the first output circuit 83, or torotate the energy 90 degrees for transmission to the second outputcircuit 86. The fixed current source 97 coupled to the external coil 96therefore provides a regulated amount of current to establish a tendencyto a 45 degree rotation of energy within the waveguide 82 through theaction of the ferromagnetic pencil 90 under the resulting static biasingmagnetic field. In conjunction with this biasing effect, however, thecurrent pulse source 95 provides the desired cancelling or augmentingmagnetic field. Here again, the volume and disposition of the variousmagnetic elements may be so selected as to provide a 45 degree rotation,through the retained magnetic field alone, when the magneticallyretentive member (in this case the pencil 90) has been driven tosaturation in the desired direction. In

12 consequence, when the applied current pulse establishes a directionof magnetization which opposes that of the fixed current source 97,there is no net magnetization of the ferromagnetic pencil 90 andmicrowave energy from the source is transmitted through the circularwaveguide 32 to the first output circuit 83.

On the other hand, when the current pulse source establishes a fieldwhich augments the static biasing field of the fixed current source 97,a total rotation of degrees is provided, and the energy is transmittedout the second output circuit 86. In the present example, the +45 degreerotation is taken as that which is clockwise looking from the input endtoward the output end, although the rotation can be in either directionby arrangement of the field direction and the ferromagnetic elementposition. Among the advantages of this arrangement are the fact that afull 90 degree rotation may be provided without extensive current drainor an excessive length of ferromagnetic pencil. The fixed current source97 is not required to be a switched source, so that it may be regulatedprecisely without requiring complicated additional circuitry. With thisarrangement, the net magnetic field for switching is very quicklyestablished but at the same time very precise. Here again, the action ofthe coil 96 in conjunction with the magnetic gap between the return pathcylinder 92 and the ferromagnetic pencil 90 is of importance. Thebiasing field through the ferromagnetic pencil 90 is readily establishedbut does not interfere with the establishment of the switching fieldthrough the use of pulses.

It will be apparent that a number of different arrangements may be usedto provide the self-retained magnetic flux in conjunction with thedriving pulse circuit. In FIG. 10 is illustrated an arrangement in whichenergy within a circular waveguide 100 is rotated by a composite element101. The composite element may consist as shown of ferrite end portions102 and 103 which are joined to a magnetizable center portion 104 whichis or is not active in the Faraday rotation sense, but which combineswith the tapered end portions 102 and 103 to establish the desiredmagnetic field. The pencil 101 may be held in place by dielectricsupport members 91 and may be encompassed, outside the waveguide 100 bya driving coil 106, the terminals of the coil 106 being coupled to thepulsing circuit 42. In this arrangement, the magnetizable center portion104 of the Faraday rotation pencil 101 is selected to have the desiredmagnetic retentivity to provide a given amount of Faraday rotation ofmicrowave energy. Accordingly, this arrangement, like those previouslydescribed, need only be pulsed to establish the static magnetic fieldwhich will provide the desired rotation. The advantages of thisarrangement include its compactness and ease of manufacture.

A different arrangement which may utilize an internal ferromagneticelement configuration of a largely conventional nature is shown in FIG.11. In FIG. 11, it may be seen that there is a simplified representationof a ferromagnetic pencil 108 supported centrally within a circularwaveguide 100 for providing Faraday rotation of microwave energy. Thedesired axial magnetic field may in this instance be provided by a pairof magnetizable U-shaped couplers 109, 110, each affixed to thewaveguide 100 at points adjacent the opposite ends of the ferromagneticpencil 108. The magnetizable couplers 109, 110 in this example are theelements having magnetic retentivity. A magnetizing coil 11 1 and 112encompasses the different magnetizable couplers 109 and 110, each of themagnetizing coils 111 and 112 being coupled to a pulse circuit 42. Uponapplication of a pulsing current to the coils 111 and 112 a staticmagnetic field is established through the retentivity of themagnetizable couplers 109 and 110 such that an axial magnetic fieldexists through the ferromagnetic pencil 108. Accordingly, Faradayrotation is again achieved which is accurate and reliable. Thearrangements of 13 both FIGS. and l l can be utilized in the differentconfigurations previously described, with or without static biasingfields, and for various circulating or switching purposes.

The principles of the present invention may also be utilized in othermicrowave devices which utilize the gyromagnetic nature of magnetizedferromagnetic materials. In all such devices there may be considered tobe a gyromagnetic displacement of energy whether the energy is rotated,phase shifted or absorbed. A number of devices are available whichemploy ferrites within rectangular waveguides for phase shift and otherpurposes. Some such devices utilize a centrally disposed ferritesubjected to an axial magnetic field, while others employ ferriteelements positioned asymmetrically with respect to the broad walls ofthe waveguide. The principles of the invention may be utilized witheither of these arrangements.

An example of such an arrangement is shown in FIG. 12, and consists ofthe type of transverse field phase shifter with rectangular waveguidewhich employs a ferrite in the form of a slab 118 extending normal toand between the broad Walls of a rectangular waveguide 120. Thisarrangement is merely illustrative of the class of devices, some ofwhich use individual strips of ferrite against each of the broad walls.With this arrangement may be em ployed a pair of external pole pieces121 which lie in the plane of the ferrite slab 118 but extend outwardlyfrom the waveguide 120. A substantial portion of the fiux path for theferrite slab 118 and transverse to the broad walls of the waveguide 120may be provided by a pair of external magnets. A C-shaped electromagnet12.3 on one side of the waveguide 120 may have its opposite extremitiesoperatively coupled to the different pole pieces 121. A magnetizing coil125 about the principal leg of the C-shaped magnet 121 may provide, whenenergized, the desired transverse magnetic field through the ferriteslab 118. Either the flux path completing member 123 or the ferrite slab1 18 may be of the desired retentive magnetic properties, as outlinedabove. Pulse signals may be applied to the driving coil 125' from apulse circuit 4 2.

In conjunction with this arrangement may be utilized a permanent biasingmagnet 127 of roughly horseshoe configuration. The permanent magnet 127may have each of its open ends in operative relation to a different oneof the pole pieces 121, to provide a biasing magnetic field of desireddensity and direction through the ferrite slab 118. The retained field,after saturation, and the biasing field are selected to add to a desiredamount for one direction of saturation and to cancel each other in theopposite direction. In this arrangement also the static bia ing throughthe ferrite slab 118 is made more useful by the use of a gap in thestatic biasing magnetic circuit, by spacing of the ends of the permanentmagnet 127 from the pole pieces 121.

The arrangement of FIG. 12 operates to provide what may be considered tobe an incremental phase shift of microwave energy along the waveguide120. The manner in which the transverse field phase shifter operates iswell known and need not be further described. With a biasing fieldselected with relation to the retained field, however, the applicationof a pulse from the pulse circuit 42 sufiicient to provide saturationwill indefinitely thereafter cause a predetermined amount of phase shiftalong the waveguide 120. When no phase shift is desired the pulsecircuit 42 need only provide an opposite pulse, so that the retained andbiasing fields cancel. The utility of such an arrangement is readilyapparent. Not only can such devices be utilized for controlled switchingin circulator arrangements, but a number of incremental phase shifts maybe combined to provide a total amount of phase shift of a closelycontrolled amount.

Thus there has been described an improved microwave Faraday rotationdevice which utilizes the retentivity of magnetic materials togetherwith momentary current pulses to provide phase shifting and rotation ofmicrowave energy utilizing ferromagnetic materials. Devices constructedin accordance with this principle operate precisely without highcurrentrequirements or without a need for accurate current regulation.

What is claimed is:

1. A microwave switching device comprising hollow waveguide means forpropagating electromagnetic energy; magnetizable means including aferromagnetic element disposed within said waveguide, and furtherincluding a magnetizable return path element at least partiallyencompassing said ferromagnetic element but providing a gap in themagnetic flux return path of said ferromagnetic element, at least aportion of said magnetizable means having sufiicient magneticretentivity to magnetize said ferromagnetic element to a selecteddegree; coil means disposed adjacent and magnetically coupled to saidmagnetizable means; and current pulsing means coupled to and supplyingsaid coil means with a driving current having a magnitude to providemomentary saturation magnetization in that portion of said magnetizablemeans having magnetic retentivity.

2. A microwave switching device comprising hollow waveguide means forpropagating electromagnetic energy; magnetizable means including aferromagnetic element disposed within said waveguide, and furtherincluding a magnetizable return path element at least partiallyencompassing said ferromagnetic element but providing a gap in themagnetic flux return path of said ferromagnetic element, at least aportion of said magnetizable means having sulficient magneticretentivity to magnetize said ferromagnetic element to a selecteddegree; static magnetic means magnetically coupled to said magnetizablemeans and supplying a magnetic biasing field of a selected density anddirection to said magnetizable means; coil means disposed adjacent andmagnetically coupled to said magnetizable means; and current pulsingmeans coupled to and supplying said coil means with a driving currenthaving a magnitude to provide momentary saturation magnetization in thatportion of said magnetizable means having magnetic retentivity.

3. A microwave switching device comprising hollow waveguide means havinga closed conducting end portion for reflecting electromagnetic energy,said hollow waveguide being capable of supporting plane polarized microwave electromagnetic energy in various positions of rotation ofpolarization; waveguide means including a pair of polarization sensitiveterminals for transmitting separately energy in positions of rotationwhich are orthogonal with respect to each other and rectangular with agiven plane of polarization in said hollow waveguide; magnetizable meansincluding a ferromagnetic element disposed centrally within said hollowwaveguide and in contact with said closed conducting end portion, andfurther including a magnetizable return path element at least partiallyencompassing said ferromagnetic element but providing a gap in themagnetic flux return path of said ferromagnetic element, at least aportion of said magnetizable means having suflicient magneticretentivity to magnetize said ferromagnetic element to a selecteddegree; coil means disposed adjacent and magnetically coupled to saidmagnetizable means; and current pulsing means coupled to and supplyingsaid coil means with a driving current having a magnitude to providemomentary saturation magnetization in that portion of said magnetizablemeans having magnetic retentivity.

4. A device according to claim 3, wherein said device further includesstatic magnetic means magnetically coupled to said magnetizabl-e meansand supplying a magnetic biasing field of a density and direction tocancel substantially all said magnetic retentivity only in one directionof magnetization.

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2,197,123 King Apr. 16, 1940 2,719,274 Luhrs Sept. 27, 1955 5 55 ,1912,776,412 Sparling Jan. 1, 1957 2,817,812 Fox Dec. 24, 1957 2,820,200 DuPre Jan. 14, 1958 2,844,789 Allen July 22, 1958 2,850,705 Chait et 'al.Sept. 2, 1958 10 2,884,600 FOX Apr. 28, 1959 2,887,664 Hogan May 19,1959 16 Sullivan et a1. Oct. 13, 1959 Pay Dec. 20, 1960 FOREIGN PATENTSItaly 1- Feb. 2, 1957 OTHER REFERENCES Proceedings of the I.R.E., August1958, page 1538.

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Uebele: 1957 IRE National Convention Record- Part 1, pages 227-234.

